In the manufacture of records such as audio records or the newer type of video disc, the initial step in the manufacturing process is to cut a recording of the information desired to be molded into the record into a recording substrate. Recordings for audio records are generally cut into a wax or lacquer substrate. Other types of records which have smaller signal elements, such as video discs, are generally cut into metal substrates.
The recorded substrate is then replicated in a matrixing process. The surface of a wax or lacquer recording substrate is activated and then a thin layer of a conductive material is applied to the surface of the substrate as, for example, by electroless plating. Thereafter, a metal, typically nickel, is electrodeposited on the recorded substrate until a predetermined thickness of metal is deposited. The electroformed part thus prepared is separated from the wax or lacquer substrate and is used as a master in the subsequent matrixing steps.
The procedure which is used for making replicas from metal recording substrate is slightly different. The surface of the metal recording substrate is passivated to prevent the adhesion of electroplated metal to the metal substrate. Thereafter, a metal, such as nickel, is electrodeposited on the surface of the metal recording substrate. When a sufficient thickness of metal has built up on the substrate the resulting electroformed part is separated from the metal recording substrate and is thereafter used as the master in subsequent matrixing steps.
Once the masters are obtained, the matrixing processes employed for further replication are generally similar for various types of records. The masters are mounted on revolvable cathode masks in an electroforming apparatus. The cathode mask with the master secured to it is immersed into the electrolyte solution and revolved in the solution while a metal is electroformed onto the master. The metal is electroplated onto the masters until sufficient thickness of metal is deposited so as to provide an electroformed part referred to as a mold. The molds are in turn replicated in an additional electroforming step to form a new series of parts referred to as stampers. The stampers are subsequently used in the pressing of records.
A number of problems have been encountered in the matrixing processes. When the masters are mounted on the revolving cathode mask to form a mold, or when the molds are mounted on the revolving cathode mask to form a stamper, it is extremely important that the part which is to be replicated, hereinafter referred to as the matrix, be properly positioned and sealed in a liquid tight fit to the cathode mask. The matrix must be mounted flush onto the cathode mask. The outer edge and the center hole of the matrix must be sealed liquid tight to the cathode mask to prevent electrolyte from flowing behind the matrix.
The problems presented when sealing the center hole are much more difficult to overcome than those presented when sealing the outer edge of the matrix to the cathode mask. The electrical contact of the cathode to the matrix is made at the center portion of the matrix. The center portion of the matrix should be in full flush contact with the exposed metal surface of the cathode. If full contact is not established and maintained at the center portion, high electrical resistance develops which causes burn outs and treeing about the center hole. The problems encountered in making good electrical contact between the cathode and the matrix are made more difficult because of the relatively small area available for making the electrical connection at the center portion of the matrix.
A further problem encountered at the center hole is that if a liquid tight seal is not made about the center hole, electrolyte which is used in the plating bath will flow through the center hole to the reverse side of the matrix causing plating on the back of the matrix and eventually distortion of the matrix or electrolytic errosion of the matrix.
Various suggestions have been made in prior art to improve the electrical contact and prevent leakage at the center hole. Suggestions were made, for example, to solder brass strips to the matrix being duplicated to improve the electrical contact of the matrix with the cathode. This technique was unsatisfactory as it was both costly and did not provide consistent satisfactory results. Suggestions were also made to use rubber plugs, and the like, to seal the center hole. This suggestion did not prove to be effective in preventing leakage of the electrolyte of the back of the matrix in part because of the irregularity in the size of the center hole. It was also suggested to use metal screws, and the like, at the center hole to secure the matrix to the cathode mask. However, in practice the screws, and other mechanical fasteners, allow electrolyte leakage and were plated over during electroforming causing considerable problems in separating the electroformed part from the matrix. A further suggestion was made by Hunting et al. in U.S. Pat. No. 2,890,160, issued June 9, 1959; entitled, FIXTURE SUSPENDING PHONOGRAPH RECORD BLANK. Hunting et al. suggested the use of a rubber cathode mask having a metal backup plate at the rear thereof, and using a metal screw to form a compression seal of the matrix to the face of the rubber cathode mask at the center hole. This suggestion, like the others heretofore made did not prove to be satisfactory in practice because of the relatively poor seal made at the center hole, and also because of problems caused by plating over the metal screw used to attach the matrix to the rubber cathode mask.
What would be highly advantageous would be a device for attaching the matrix to the cathode which would make a secure electrical contact of the matrix to the cathode; and which would further include the means to prevent the flow of electrolyte from the electrolytic bath through the center hole of the matrix.